DESCRIPTION: Hearing-impaired listeners and cochlear implant users have difficulty selectively attending to a sound source in environments with multiple, competing sound sources. In contrast, normal-hearing listeners are able to selectively attend to a talker of interest in a sea of competing sources, shifting attention as the need arises. The long-term objective of this project is to develop strategies and devices to help impaired listeners communicate effectively in everyday social settings that require selective attention. The current proposal is built on the hypothesis that some of the difficulty that impaired listeners have in complex environments stems from difficulties in properly forming auditory objects (i.e., grouping sound coming from one physical source into a single perceptual entity). Because interactions between auditory grouping and auditory perception are poorly understood, a necessary first step towards our long-term objective is to understand how the grouping of sound into objects affects perception in normal-hearing listeners. We will perform psychophysical experiments in normal- hearing listeners that test how grouping influences auditory perception and use computational models to understand the processes that normally affect how listeners attend to one source in a mixture of competing sound sources. The specific aims of this project explore how perceptual grouping influences perceptual sensitivity to basic psychophysical sound attributes (Aims 1 and 2) as well as the ability to understand speech when there is a competing, similar sound source (Aim 3). Aim 1 explores how sensitivity to spatial cues and the intensity of one tone can be degraded when that tone is perceptually integrated into an object containing other sounds. Aim 2 explores how the ability to extract the spectro-temporal pattern defined by multiple simultaneous or sequential target tones (e.g., spectral profile, rhythm, pitch contour) can be degraded when competing sounds interfere with the perceptual grouping of the target tones into a perceptual object. Aim 3 measures how weakened grouping cues (like those commonly experienced with hearing impairment or through a cochlear implant) interfere with speech intelligibility in the presence of a competing sound object. Together, the proposed studies test a unified conceptual model of why perceptual grouping directly influences the ability to communicate in the complex social settings, from heated business meetings to lively dinner parties. PUBLIC HEALTH RELEVANCE One of the most common complaints of hearing aid and cochlear implant users is that they cannot communicate effectively in everyday settings where there are multiple, competing sound sources. This problem often causes social isolation, as listeners opt out of trying to participate in complex settings rather than facing frustration and failure. Understanding the processes that allow normal- hearing listeners to cope with complex acoustic environments is a critical and necessary step towards developing signal-processing schemes and devices to ameliorate the difficulties facing impaired listeners.